[PATCH v2 0/9] fallocate: introduce FALLOC_FL_WRITE_ZEROES flag

[PATCH v2 0/9] fallocate: introduce FALLOC_FL_WRITE_ZEROES flag

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

Changes since v1:
 - Rebase codes on 6.16-rc2.
 - Use max_{hw|user}_wzeroes_unmap_sectors queue limits instead of
   BLK_FEAT_WRITE_ZEROES_UNMAP feature to represent the status of the
   unmap write zeroes operation as Christoph and Darrick suggested. This
   redoes the first 5 patches, so remove all the reviewed-by tags,
   please review them again.
 - Simplify the description of FALLOC_FL_WRITE_ZEROES in patch 06 as
   Darrick suggested.
 - Revise the check order of FALLOC_FL_WRITE_ZEROES in patch 08 as
   Christoph suggested.
Changes since RFC v4:
 - Rebase codes on 6.16-rc1.
 - Add a new queue_limit flag, and change the write_zeroes_unmap sysfs
   interface to RW mode. User can disable the unmap write zeroes
   operation by writing '0' to it when the operation is slow.
 - Modify the documentation of write_zeroes_unmap sysfs interface as
   Martin suggested.
 - Remove the statx interface.
 - Make the bdev and ext4 don't allow to submit FALLOC_FL_WRITE_ZEROES
   if the block device does not enable the unmap write zeroes operation,
   it should return -EOPNOTSUPP.
Changes sicne RFC v3:
 - Rebase codes on 6.15-rc2.
 - Add a note in patch 1 to indicate that the unmap write zeros command
   is not always guaranteed as Christoph suggested.
 - Rename bdev_unmap_write_zeroes() helper and move it to patch 1 as
   Christoph suggested.
 - Introduce a new statx attribute flag STATX_ATTR_WRITE_ZEROES_UNMAP as
   Christoph and Christian suggested.
 - Exchange the order of the two patches that modified
   blkdev_fallocate() as Christoph suggested.
Changes since RFC v2:
 - Rebase codes on next-20250314.
 - Add support for nvme multipath.
 - Add support for NVMeT with block device backing.
 - Clear FALLOC_FL_WRITE_ZEROES if dm clear
   limits->max_write_zeroes_sectors.
 - Complement the counterpart userspace tools(util-linux and xfs_io)
   and tests(blktests and xfstests), please see below for details.
Changes since RFC v1:
 - Switch to add a new write zeroes operation, FALLOC_FL_WRITE_ZEROES,
   in fallocate, instead of just adding a supported flag to
   FALLOC_FL_ZERO_RANGE.
 - Introduce a new flag BLK_FEAT_WRITE_ZEROES_UNMAP to the block
   device's queue limit features, and implement it on SCSI sd driver,
   NVMe SSD driver and dm driver.
 - Implement FALLOC_FL_WRITE_ZEROES on both the ext4 filesystem and
   block device (bdev).

v1:     https://lore.kernel.org/linux-fsdevel/20250604020850.1304633-1-yi.zhang@huaweicloud.com/
RFC v4: https://lore.kernel.org/linux-fsdevel/20250421021509.2366003-1-yi.zhang@huaweicloud.com/
RFC v3: https://lore.kernel.org/linux-fsdevel/20250318073545.3518707-1-yi.zhang@huaweicloud.com/
RFC v2: https://lore.kernel.org/linux-fsdevel/20250115114637.2705887-1-yi.zhang@huaweicloud.com/
RFC v1: https://lore.kernel.org/linux-fsdevel/20241228014522.2395187-1-yi.zhang@huaweicloud.com/

The counterpart userspace tools changes and tests are here:
 - util-linux: https://lore.kernel.org/linux-fsdevel/20250318073218.3513262-1-yi.zhang@huaweicloud.com/ 
 - xfsprogs: https://lore.kernel.org/linux-fsdevel/20250318072318.3502037-1-yi.zhang@huaweicloud.com/
 - xfstests: https://lore.kernel.org/linux-fsdevel/20250318072615.3505873-1-yi.zhang@huaweicloud.com/
   (needs to be updated)
 - blktests: https://lore.kernel.org/linux-fsdevel/20250318072835.3508696-1-yi.zhang@huaweicloud.com/
   (needs to be updated)

Original Description:

Currently, we can use the fallocate command to quickly create a
pre-allocated file. However, on most filesystems, such as ext4 and XFS,
fallocate create pre-allocation blocks in an unwritten state, and the
FALLOC_FL_ZERO_RANGE flag also behaves similarly. The extent state must
be converted to a written state when the user writes data into this
range later, which can trigger numerous metadata changes and consequent
journal I/O. This may leads to significant write amplification and
performance degradation in synchronous write mode. Therefore, we need a
method to create a pre-allocated file with written extents that can be
used for pure overwriting. At the monent, the only method available is
to create an empty file and write zero data into it (for example, using
'dd' with a large block size). However, this method is slow and consumes
a considerable amount of disk bandwidth, we must pre-allocate files in
advance but cannot add pre-allocated files while user business services
are running.

Fortunately, with the development and more and more widely used of
flash-based storage devices, we can efficiently write zeros to SSDs
using the unmap write zeroes command if the devices do not write
physical zeroes to the media. For example, if SCSI SSDs support the
UMMAP bit or NVMe SSDs support the DEAC bit[1], the write zeroes command
does not write actual data to the device, instead, NVMe converts the
zeroed range to a deallocated state, which works fast and consumes
almost no disk write bandwidth. Consequently, this feature can provide
us with a faster method for creating pre-allocated files with written
extents and zeroed data. However, please note that this may be a
best-effort optimization rather than a mandatory requirement, some
devices may partially fall back to writing physical zeroes due to
factors such as receiving unaligned commands. 

This series aims to implement this by:
1. Introduce a new feature BLK_FEAT_WRITE_ZEROES_UNMAP to the block
   device queue limit features, which indicates whether the storage is
   device explicitly supports the unmapped write zeroes command. This
   flag should be set to 1 by the driver if the attached disk supports
   this command.

2. Introduce a queue limit flag, BLK_FLAG_WRITE_ZEROES_UNMAP_DISABLED,
   along with a corresponding sysfs entry. Users can query the support
   status of the unmap write zeroes operation and disable this operation
   if the write zeroes operation is very slow.

       /sys/block/<disk>/queue/write_zeroes_unmap

3. Introduce a new flag, FALLOC_FL_WRITE_ZEROES, into the fallocate.
   Filesystems that support this operation should allocate written
   extents and issue zeroes to the specified range of the device. For
   local block device filesystems, this operation should depend on the
   write_zeroes_unmap operaion of the underlying block device. It should
   return -EOPNOTSUPP if the device doesn't enable unmap write zeroes
   operaion.

This series implements the BLK_FEAT_WRITE_ZEROES_UNMAP feature and
BLK_FLAG_WRITE_ZEROES_UNMAP_DISABLED flag for SCSI, NVMe and
device-mapper drivers, and add the FALLOC_FL_WRITE_ZEROES and
STATX_ATTR_WRITE_ZEROES_UNMAP support for ext4 and raw bdev devices.
Any comments are welcome.

I've tested performance with this series on ext4 filesystem on my
machine with an Intel Xeon Gold 6248R CPU, a 7TB KCD61LUL7T68 NVMe SSD
which supports unmap write zeroes command with the Deallocated state
and the DEAC bit. Feel free to give it a try.

0. Ensure the NVMe device supports WRITE_ZERO command.

 $ cat /sys/block/nvme5n1/queue/write_zeroes_max_bytes
   8388608
 $ nvme id-ns -H /dev/nvme5n1 | grep -i -A 3 "dlfeat"
   dlfeat  : 25
   [4:4] : 0x1   Guard Field of Deallocated Logical Blocks is set to CRC
                 of The Value Read
   [3:3] : 0x1   Deallocate Bit in the Write Zeroes Command is Supported
   [2:0] : 0x1   Bytes Read From a Deallocated Logical Block and its
                 Metadata are 0x00

1. Compare 'dd' and fallocate with unmap write zeroes, the later one is
   significantly faster than 'dd'.

   Create a 1GB and 10GB zeroed file.
    $dd if=/dev/zero of=foo bs=2M count=$count oflag=direct
    $time fallocate -w -l $size bar

    #1G
    dd:                     0.5s
    FALLOC_FL_WRITE_ZEROES: 0.17s

    #10G
    dd:                     5.0s
    FALLOC_FL_WRITE_ZEROES: 1.7s

2. Run fio overwrite and fallocate with unmap write zeroes
   simultaneously, fallocate has little impact on write bandwidth and
   only slightly affects write latency.

 a) Test bandwidth costs.
  $ fio -directory=/test -direct=1 -iodepth=10 -fsync=0 -rw=write \
        -numjobs=10 -bs=2M -ioengine=libaio -size=20G -runtime=20 \
        -fallocate=none -overwrite=1 -group_reportin -name=bw_test

   Without background zero range:
    bw (MiB/s): min= 2068, max= 2280, per=100.00%, avg=2186.40

   With background zero range:
    bw (MiB/s): min= 2056, max= 2308, per=100.00%, avg=2186.20

 b) Test write latency costs.
  $ fio -filename=/test/foo -direct=1 -iodepth=1 -fsync=0 -rw=write \
        -numjobs=1 -bs=4k -ioengine=psync -size=5G -runtime=20 \
        -fallocate=none -overwrite=1 -group_reportin -name=lat_test

   Without background zero range:
   lat (nsec): min=9269, max=71635, avg=9840.65

   With a background zero range:
   lat (usec): min=9, max=982, avg=11.03

3. Compare overwriting in a pre-allocated unwritten file and a written
   file in O_DSYNC mode. Write to a file with written extents is much
   faster.

  # First mkfs and create a test file according to below three cases,
  # and then run fio.

  $ fio -filename=/test/foo -direct=1 -iodepth=1 -fdatasync=1 \
        -rw=write -numjobs=1 -bs=4k -ioengine=psync -size=5G \
        -runtime=20 -fallocate=none -group_reportin -name=test

   unwritten file:                 IOPS=20.1k, BW=78.7MiB/s
   unwritten file + fast_commit:   IOPS=42.9k, BW=167MiB/s
   written file:                   IOPS=98.8k, BW=386MiB/s

Thanks,
Yi.

---

[1] https://nvmexpress.org/specifications/
    NVM Command Set Specification, Figure 82 and Figure 114.

Zhang Yi (9):
  block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits
  nvme: set max_hw_wzeroes_unmap_sectors if device supports DEAC bit
  nvmet: set WZDS and DRB if device enables unmap write zeroes operation
  scsi: sd: set max_hw_wzeroes_unmap_sectors if device supports
    SD_ZERO_*_UNMAP
  dm: clear unmap write zeroes limits when disabling write zeroes
  fs: introduce FALLOC_FL_WRITE_ZEROES to fallocate
  block: factor out common part in blkdev_fallocate()
  block: add FALLOC_FL_WRITE_ZEROES support
  ext4: add FALLOC_FL_WRITE_ZEROES support

 Documentation/ABI/stable/sysfs-block | 33 ++++++++++++++
 block/blk-settings.c                 | 20 ++++++++-
 block/blk-sysfs.c                    | 26 +++++++++++
 block/fops.c                         | 44 +++++++++++--------
 drivers/md/dm-table.c                |  4 +-
 drivers/nvme/host/core.c             | 20 +++++----
 drivers/nvme/target/io-cmd-bdev.c    |  4 ++
 drivers/scsi/sd.c                    |  5 +++
 fs/ext4/extents.c                    | 66 +++++++++++++++++++++++-----
 fs/open.c                            |  1 +
 include/linux/blkdev.h               | 10 +++++
 include/linux/falloc.h               |  3 +-
 include/trace/events/ext4.h          |  3 +-
 include/uapi/linux/falloc.h          | 17 +++++++
 14 files changed, 212 insertions(+), 44 deletions(-)

-- 
2.46.1

[PATCH v2 1/9] block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

Currently, disks primarily implement the write zeroes command (aka
REQ_OP_WRITE_ZEROES) through two mechanisms: the first involves
physically writing zeros to the disk media (e.g., HDDs), while the
second performs an unmap operation on the logical blocks, effectively
putting them into a deallocated state (e.g., SSDs). The first method is
generally slow, while the second method is typically very fast.

For example, on certain NVMe SSDs that support NVME_NS_DEAC, submitting
REQ_OP_WRITE_ZEROES requests with the NVME_WZ_DEAC bit can accelerate
the write zeros operation by placing disk blocks into a deallocated
state, which opportunistically avoids writing zeroes to media while
still guaranteeing that subsequent reads from the specified block range
will return zeroed data. This is a best-effort optimization, not a
mandatory requirement, some devices may partially fall back to writing
physical zeroes due to factors such as misalignment or being asked to
clear a block range smaller than the device's internal allocation unit.
Therefore, the speed of this operation is not guaranteed.

It is difficult to determine whether the storage device supports unmap
write zeroes operation. We cannot determine this by only querying
bdev_limits(bdev)->max_write_zeroes_sectors. Therefore, first, add a new
hardware queue limit parameters, max_hw_wzeroes_unmap_sectors, to
indicate whether a device supports this unmap write zeroes operation.
Then, add two new counterpart software queue limits,
max_wzeroes_unmap_sectors and max_user_wzeroes_unmap_sectors, which
allow users to disable this operation if the speed is very slow on some
sepcial devices.

Finally, for the stacked devices cases, initialize these two parameters
to UINT_MAX. This operation should be enabled by both the stacking
driver and all underlying devices.

Thanks to Martin K. Petersen for optimizing the documentation of the
write_zeroes_unmap sysfs interface.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 Documentation/ABI/stable/sysfs-block | 33 ++++++++++++++++++++++++++++
 block/blk-settings.c                 | 20 +++++++++++++++--
 block/blk-sysfs.c                    | 26 ++++++++++++++++++++++
 include/linux/blkdev.h               | 10 +++++++++
 4 files changed, 87 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index 4ba771b56b3b..803f578dc023 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -778,6 +778,39 @@ Description:
 		0, write zeroes is not supported by the device.
 
 
+What:		/sys/block/<disk>/queue/write_zeroes_unmap_max_hw_bytes
+Date:		January 2025
+Contact:	Zhang Yi <yi.zhang@huawei.com>
+Description:
+		[RO] This file indicates whether a device supports zeroing data
+		in a specified block range without incurring the cost of
+		physically writing zeroes to the media for each individual
+		block. If this parameter is set to write_zeroes_max_bytes, the
+		device implements a zeroing operation which opportunistically
+		avoids writing zeroes to media while still guaranteeing that
+		subsequent reads from the specified block range will return
+		zeroed data. This operation is a best-effort optimization, a
+		device may fall back to physically writing zeroes to the media
+		due to other factors such as misalignment or being asked to
+		clear a block range smaller than the device's internal
+		allocation unit. If this parameter is set to 0, the device may
+		have to write each logical block media during a zeroing
+		operation.
+
+
+What:		/sys/block/<disk>/queue/write_zeroes_unmap_max_bytes
+Date:		January 2025
+Contact:	Zhang Yi <yi.zhang@huawei.com>
+Description:
+		[RW] While write_zeroes_unmap_max_hw_bytes is the hardware limit
+		for the device, this setting is the software limit. Since the
+		unmap write zeroes operation is a best-effort optimization, some
+		devices may still physically writing zeroes to media. So the
+		speed of this operation is not guaranteed. Writing a value of
+		'0' to this file disables this operation. Otherwise, this
+		parameter should be equal to write_zeroes_unmap_max_hw_bytes.
+
+
 What:		/sys/block/<disk>/queue/zone_append_max_bytes
 Date:		May 2020
 Contact:	linux-block@vger.kernel.org
diff --git a/block/blk-settings.c b/block/blk-settings.c
index a000daafbfb4..b5c75f0ac3e9 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -50,6 +50,8 @@ void blk_set_stacking_limits(struct queue_limits *lim)
 	lim->max_sectors = UINT_MAX;
 	lim->max_dev_sectors = UINT_MAX;
 	lim->max_write_zeroes_sectors = UINT_MAX;
+	lim->max_hw_wzeroes_unmap_sectors = UINT_MAX;
+	lim->max_user_wzeroes_unmap_sectors = UINT_MAX;
 	lim->max_hw_zone_append_sectors = UINT_MAX;
 	lim->max_user_discard_sectors = UINT_MAX;
 }
@@ -333,6 +335,12 @@ int blk_validate_limits(struct queue_limits *lim)
 	if (!lim->max_segments)
 		lim->max_segments = BLK_MAX_SEGMENTS;
 
+	if (lim->max_hw_wzeroes_unmap_sectors &&
+	    lim->max_hw_wzeroes_unmap_sectors != lim->max_write_zeroes_sectors)
+		return -EINVAL;
+	lim->max_wzeroes_unmap_sectors = min(lim->max_hw_wzeroes_unmap_sectors,
+			lim->max_user_wzeroes_unmap_sectors);
+
 	lim->max_discard_sectors =
 		min(lim->max_hw_discard_sectors, lim->max_user_discard_sectors);
 
@@ -418,10 +426,11 @@ int blk_set_default_limits(struct queue_limits *lim)
 {
 	/*
 	 * Most defaults are set by capping the bounds in blk_validate_limits,
-	 * but max_user_discard_sectors is special and needs an explicit
-	 * initialization to the max value here.
+	 * but these limits are special and need an explicit initialization to
+	 * the max value here.
 	 */
 	lim->max_user_discard_sectors = UINT_MAX;
+	lim->max_user_wzeroes_unmap_sectors = UINT_MAX;
 	return blk_validate_limits(lim);
 }
 
@@ -708,6 +717,13 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 	t->max_dev_sectors = min_not_zero(t->max_dev_sectors, b->max_dev_sectors);
 	t->max_write_zeroes_sectors = min(t->max_write_zeroes_sectors,
 					b->max_write_zeroes_sectors);
+	t->max_user_wzeroes_unmap_sectors =
+			min(t->max_user_wzeroes_unmap_sectors,
+			    b->max_user_wzeroes_unmap_sectors);
+	t->max_hw_wzeroes_unmap_sectors =
+			min(t->max_hw_wzeroes_unmap_sectors,
+			    b->max_hw_wzeroes_unmap_sectors);
+
 	t->max_hw_zone_append_sectors = min(t->max_hw_zone_append_sectors,
 					b->max_hw_zone_append_sectors);
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index b2b9b89d6967..48c7ecbb531f 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -161,6 +161,8 @@ static ssize_t queue_##_field##_show(struct gendisk *disk, char *page)	\
 QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(max_discard_sectors)
 QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(max_hw_discard_sectors)
 QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(max_write_zeroes_sectors)
+QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(max_hw_wzeroes_unmap_sectors)
+QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(max_wzeroes_unmap_sectors)
 QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(atomic_write_max_sectors)
 QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(atomic_write_boundary_sectors)
 QUEUE_SYSFS_LIMIT_SHOW_SECTORS_TO_BYTES(max_zone_append_sectors)
@@ -205,6 +207,24 @@ static int queue_max_discard_sectors_store(struct gendisk *disk,
 	return 0;
 }
 
+static int queue_max_wzeroes_unmap_sectors_store(struct gendisk *disk,
+		const char *page, size_t count, struct queue_limits *lim)
+{
+	unsigned long max_zeroes_bytes, max_hw_zeroes_bytes;
+	ssize_t ret;
+
+	ret = queue_var_store(&max_zeroes_bytes, page, count);
+	if (ret < 0)
+		return ret;
+
+	max_hw_zeroes_bytes = lim->max_hw_wzeroes_unmap_sectors << SECTOR_SHIFT;
+	if (max_zeroes_bytes != 0 && max_zeroes_bytes != max_hw_zeroes_bytes)
+		return -EINVAL;
+
+	lim->max_user_wzeroes_unmap_sectors = max_zeroes_bytes >> SECTOR_SHIFT;
+	return 0;
+}
+
 static int
 queue_max_sectors_store(struct gendisk *disk, const char *page, size_t count,
 		struct queue_limits *lim)
@@ -514,6 +534,10 @@ QUEUE_LIM_RO_ENTRY(queue_atomic_write_unit_min, "atomic_write_unit_min_bytes");
 
 QUEUE_RO_ENTRY(queue_write_same_max, "write_same_max_bytes");
 QUEUE_LIM_RO_ENTRY(queue_max_write_zeroes_sectors, "write_zeroes_max_bytes");
+QUEUE_LIM_RO_ENTRY(queue_max_hw_wzeroes_unmap_sectors,
+		"write_zeroes_unmap_max_hw_bytes");
+QUEUE_LIM_RW_ENTRY(queue_max_wzeroes_unmap_sectors,
+		"write_zeroes_unmap_max_bytes");
 QUEUE_LIM_RO_ENTRY(queue_max_zone_append_sectors, "zone_append_max_bytes");
 QUEUE_LIM_RO_ENTRY(queue_zone_write_granularity, "zone_write_granularity");
 
@@ -662,6 +686,8 @@ static struct attribute *queue_attrs[] = {
 	&queue_atomic_write_unit_min_entry.attr,
 	&queue_atomic_write_unit_max_entry.attr,
 	&queue_max_write_zeroes_sectors_entry.attr,
+	&queue_max_hw_wzeroes_unmap_sectors_entry.attr,
+	&queue_max_wzeroes_unmap_sectors_entry.attr,
 	&queue_max_zone_append_sectors_entry.attr,
 	&queue_zone_write_granularity_entry.attr,
 	&queue_rotational_entry.attr,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index a59880c809c7..1a5725c1f93d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -383,6 +383,9 @@ struct queue_limits {
 	unsigned int		max_user_discard_sectors;
 	unsigned int		max_secure_erase_sectors;
 	unsigned int		max_write_zeroes_sectors;
+	unsigned int		max_wzeroes_unmap_sectors;
+	unsigned int		max_hw_wzeroes_unmap_sectors;
+	unsigned int		max_user_wzeroes_unmap_sectors;
 	unsigned int		max_hw_zone_append_sectors;
 	unsigned int		max_zone_append_sectors;
 	unsigned int		discard_granularity;
@@ -1042,6 +1045,7 @@ static inline void blk_queue_disable_secure_erase(struct request_queue *q)
 static inline void blk_queue_disable_write_zeroes(struct request_queue *q)
 {
 	q->limits.max_write_zeroes_sectors = 0;
+	q->limits.max_wzeroes_unmap_sectors = 0;
 }
 
 /*
@@ -1378,6 +1382,12 @@ static inline unsigned int bdev_write_zeroes_sectors(struct block_device *bdev)
 	return bdev_limits(bdev)->max_write_zeroes_sectors;
 }
 
+static inline unsigned int
+bdev_write_zeroes_unmap_sectors(struct block_device *bdev)
+{
+	return bdev_limits(bdev)->max_wzeroes_unmap_sectors;
+}
+
 static inline bool bdev_nonrot(struct block_device *bdev)
 {
 	return blk_queue_nonrot(bdev_get_queue(bdev));
-- 
2.46.1

[PATCH v2 2/9] nvme: set max_hw_wzeroes_unmap_sectors if device supports DEAC bit

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

When the device supports the Write Zeroes command and the DEAC bit, it
indicates that the deallocate bit in the Write Zeroes command is
supported, and the bytes read from a deallocated logical block are
zeroes. This means the device supports unmap Write Zeroes operation, so
set the max_hw_wzeroes_unmap_sectors to max_write_zeroes_sectors on the
device's queue limit.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 drivers/nvme/host/core.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 92697f98c601..90af4a15b696 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2420,22 +2420,24 @@ static int nvme_update_ns_info_block(struct nvme_ns *ns,
 	else
 		lim.write_stream_granularity = 0;
 
-	ret = queue_limits_commit_update(ns->disk->queue, &lim);
-	if (ret) {
-		blk_mq_unfreeze_queue(ns->disk->queue, memflags);
-		goto out;
-	}
-
-	set_capacity_and_notify(ns->disk, capacity);
-
 	/*
 	 * Only set the DEAC bit if the device guarantees that reads from
 	 * deallocated data return zeroes.  While the DEAC bit does not
 	 * require that, it must be a no-op if reads from deallocated data
 	 * do not return zeroes.
 	 */
-	if ((id->dlfeat & 0x7) == 0x1 && (id->dlfeat & (1 << 3)))
+	if ((id->dlfeat & 0x7) == 0x1 && (id->dlfeat & (1 << 3))) {
 		ns->head->features |= NVME_NS_DEAC;
+		lim.max_hw_wzeroes_unmap_sectors = lim.max_write_zeroes_sectors;
+	}
+
+	ret = queue_limits_commit_update(ns->disk->queue, &lim);
+	if (ret) {
+		blk_mq_unfreeze_queue(ns->disk->queue, memflags);
+		goto out;
+	}
+
+	set_capacity_and_notify(ns->disk, capacity);
 	set_disk_ro(ns->disk, nvme_ns_is_readonly(ns, info));
 	set_bit(NVME_NS_READY, &ns->flags);
 	blk_mq_unfreeze_queue(ns->disk->queue, memflags);
-- 
2.46.1

[PATCH v2 3/9] nvmet: set WZDS and DRB if device enables unmap write zeroes operation

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

Set the WZDS and DRB bits to the namespace dlfeat if the underlying
block device enables the unmap write zeroes operation, make the nvme
target device supports the unmap write zeroes command.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 drivers/nvme/target/io-cmd-bdev.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
index eba42df2f821..31d6c4a63fa5 100644
--- a/drivers/nvme/target/io-cmd-bdev.c
+++ b/drivers/nvme/target/io-cmd-bdev.c
@@ -46,6 +46,10 @@ void nvmet_bdev_set_limits(struct block_device *bdev, struct nvme_id_ns *id)
 	id->npda = id->npdg;
 	/* NOWS = Namespace Optimal Write Size */
 	id->nows = to0based(bdev_io_opt(bdev) / bdev_logical_block_size(bdev));
+
+	/* Set WZDS and DRB if device supports unmapped write zeroes */
+	if (bdev_write_zeroes_unmap_sectors(bdev))
+		id->dlfeat = (1 << 3) | 0x1;
 }
 
 void nvmet_bdev_ns_disable(struct nvmet_ns *ns)
-- 
2.46.1

[PATCH v2 4/9] scsi: sd: set max_hw_wzeroes_unmap_sectors if device supports SD_ZERO_*_UNMAP

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

When the device supports the Write Zeroes command and the zeroing mode
is set to SD_ZERO_WS16_UNMAP or SD_ZERO_WS10_UNMAP, this means that the
device supports unmap Write Zeroes, so set the corresponding
max_hw_write_zeroes_unmap_sectors to max_write_zeroes_sectors on the
device's queue limit.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 drivers/scsi/sd.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 3f6e87705b62..877dc34e8f37 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1141,6 +1141,11 @@ static void sd_config_write_same(struct scsi_disk *sdkp,
 out:
 	lim->max_write_zeroes_sectors =
 		sdkp->max_ws_blocks * (logical_block_size >> SECTOR_SHIFT);
+
+	if (sdkp->zeroing_mode == SD_ZERO_WS16_UNMAP ||
+	    sdkp->zeroing_mode == SD_ZERO_WS10_UNMAP)
+		lim->max_hw_wzeroes_unmap_sectors =
+				lim->max_write_zeroes_sectors;
 }
 
 static blk_status_t sd_setup_flush_cmnd(struct scsi_cmnd *cmd)
-- 
2.46.1

[PATCH v2 5/9] dm: clear unmap write zeroes limits when disabling write zeroes

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

The unmap write zeroes limits have been set to the stacking queue limits
by default in blk_set_stacking_limits() and blk_stack_limits(), but it
should be cleared if any underlying device does not support it.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 drivers/md/dm-table.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 24a857ff6d0b..d9d5e6aa5707 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -2065,8 +2065,10 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 		limits->discard_alignment = 0;
 	}
 
-	if (!dm_table_supports_write_zeroes(t))
+	if (!dm_table_supports_write_zeroes(t)) {
 		limits->max_write_zeroes_sectors = 0;
+		limits->max_hw_wzeroes_unmap_sectors = 0;
+	}
 
 	if (!dm_table_supports_secure_erase(t))
 		limits->max_secure_erase_sectors = 0;
-- 
2.46.1

[PATCH v2 6/9] fs: introduce FALLOC_FL_WRITE_ZEROES to fallocate

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

With the development of flash-based storage devices, we can quickly
write zeros to SSDs using the WRITE_ZERO command if the devices do not
actually write physical zeroes to the media. Therefore, we can use this
command to quickly preallocate a real all-zero file with written
extents. This approach should be beneficial for subsequent pure
overwriting within this file, as it can save on block allocation and,
consequently, significant metadata changes, which should greatly improve
overwrite performance on certain filesystems.

Therefore, introduce a new operation FALLOC_FL_WRITE_ZEROES to
fallocate. This flag is used to convert a specified range of a file to
zeros by issuing a zeroing operation. Blocks should be allocated for the
regions that span holes in the file, and the entire range is converted
to written extents. If the underlying device supports the actual offload
write zeroes command, the process of zeroing out operation can be
accelerated. If it does not, we currently don't prevent the file system
from writing actual zeros to the device. This provides users with a new
method to quickly generate a zeroed file, users no longer need to write
zero data to create a file with written extents.

Users can determine whether a disk supports the unmap write zeroes
feature through querying this sysfs interface:

    /sys/block/<disk>/queue/write_zeroes_unmap_max_hw_bytes

Users can also enable or disable the unmap write zeroes operation
through this sysfs interface:

    /sys/block/<disk>/queue/write_zeroes_unmap_max_bytes

Finally, this flag cannot be specified in conjunction with the
FALLOC_FL_KEEP_SIZE since allocating written extents beyond file EOF is
not permitted. In addition, filesystems that always require out-of-place
writes should not support this flag since they still need to allocated
new blocks during subsequent overwrites.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
---
 fs/open.c                   |  1 +
 include/linux/falloc.h      |  3 ++-
 include/uapi/linux/falloc.h | 17 +++++++++++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/open.c b/fs/open.c
index 7828234a7caa..b777e11e5522 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -281,6 +281,7 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 		break;
 	case FALLOC_FL_COLLAPSE_RANGE:
 	case FALLOC_FL_INSERT_RANGE:
+	case FALLOC_FL_WRITE_ZEROES:
 		if (mode & FALLOC_FL_KEEP_SIZE)
 			return -EOPNOTSUPP;
 		break;
diff --git a/include/linux/falloc.h b/include/linux/falloc.h
index 3f49f3df6af5..7c38c6b76b60 100644
--- a/include/linux/falloc.h
+++ b/include/linux/falloc.h
@@ -36,7 +36,8 @@ struct space_resv {
 				 FALLOC_FL_COLLAPSE_RANGE |	\
 				 FALLOC_FL_ZERO_RANGE |		\
 				 FALLOC_FL_INSERT_RANGE |	\
-				 FALLOC_FL_UNSHARE_RANGE)
+				 FALLOC_FL_UNSHARE_RANGE |	\
+				 FALLOC_FL_WRITE_ZEROES)
 
 /* on ia32 l_start is on a 32-bit boundary */
 #if defined(CONFIG_X86_64)
diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
index 5810371ed72b..1f9ca757d02d 100644
--- a/include/uapi/linux/falloc.h
+++ b/include/uapi/linux/falloc.h
@@ -78,4 +78,21 @@
  */
 #define FALLOC_FL_UNSHARE_RANGE		0x40
 
+/*
+ * FALLOC_FL_WRITE_ZEROES zeroes a specified file range in such a way that
+ * subsequent writes to that range do not require further changes to the file
+ * mapping metadata. This flag is beneficial for subsequent pure overwriting
+ * within this range, as it can save on block allocation and, consequently,
+ * significant metadata changes. Therefore, filesystems that always require
+ * out-of-place writes should not support this flag.
+ *
+ * Different filesystems may implement different limitations on the
+ * granularity of the zeroing operation. Most will preferably be accelerated
+ * by submitting write zeroes command if the backing storage supports, which
+ * may not physically write zeros to the media.
+ *
+ * This flag cannot be specified in conjunction with the FALLOC_FL_KEEP_SIZE.
+ */
+#define FALLOC_FL_WRITE_ZEROES		0x80
+
 #endif /* _UAPI_FALLOC_H_ */
-- 
2.46.1

[PATCH v2 7/9] block: factor out common part in blkdev_fallocate()

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

Only the flags passed to blkdev_issue_zeroout() differ among the two
zeroing branches in blkdev_fallocate(). Therefore, do cleanup by
factoring them out.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
---
 block/fops.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 1309861d4c2c..e1c921549d28 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -850,6 +850,7 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 	struct block_device *bdev = I_BDEV(inode);
 	loff_t end = start + len - 1;
 	loff_t isize;
+	unsigned int flags;
 	int error;
 
 	/* Fail if we don't recognize the flags. */
@@ -877,34 +878,29 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 	inode_lock(inode);
 	filemap_invalidate_lock(inode->i_mapping);
 
-	/*
-	 * Invalidate the page cache, including dirty pages, for valid
-	 * de-allocate mode calls to fallocate().
-	 */
 	switch (mode) {
 	case FALLOC_FL_ZERO_RANGE:
 	case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE:
-		error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
-		if (error)
-			goto fail;
-
-		error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
-					     len >> SECTOR_SHIFT, GFP_KERNEL,
-					     BLKDEV_ZERO_NOUNMAP);
+		flags = BLKDEV_ZERO_NOUNMAP;
 		break;
 	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE:
-		error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
-		if (error)
-			goto fail;
-
-		error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
-					     len >> SECTOR_SHIFT, GFP_KERNEL,
-					     BLKDEV_ZERO_NOFALLBACK);
+		flags = BLKDEV_ZERO_NOFALLBACK;
 		break;
 	default:
 		error = -EOPNOTSUPP;
+		goto fail;
 	}
 
+	/*
+	 * Invalidate the page cache, including dirty pages, for valid
+	 * de-allocate mode calls to fallocate().
+	 */
+	error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
+	if (error)
+		goto fail;
+
+	error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
+				     len >> SECTOR_SHIFT, GFP_KERNEL, flags);
  fail:
 	filemap_invalidate_unlock(inode->i_mapping);
 	inode_unlock(inode);
-- 
2.46.1

[PATCH v2 8/9] block: add FALLOC_FL_WRITE_ZEROES support

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

Add support for FALLOC_FL_WRITE_ZEROES, if the block device enables the
unmap write zeroes operation, it will issue a write zeroes command.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
---
 block/fops.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/fops.c b/block/fops.c
index e1c921549d28..474656a0de70 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -841,7 +841,7 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 
 #define	BLKDEV_FALLOC_FL_SUPPORTED					\
 		(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |		\
-		 FALLOC_FL_ZERO_RANGE)
+		 FALLOC_FL_ZERO_RANGE | FALLOC_FL_WRITE_ZEROES)
 
 static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 			     loff_t len)
@@ -856,6 +856,13 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 	/* Fail if we don't recognize the flags. */
 	if (mode & ~BLKDEV_FALLOC_FL_SUPPORTED)
 		return -EOPNOTSUPP;
+	/*
+	 * Don't allow writing zeroes if the device does not enable the
+	 * unmap write zeroes operation.
+	 */
+	if ((mode & FALLOC_FL_WRITE_ZEROES) &&
+	    !bdev_write_zeroes_unmap_sectors(bdev))
+		return -EOPNOTSUPP;
 
 	/* Don't go off the end of the device. */
 	isize = bdev_nr_bytes(bdev);
@@ -886,6 +893,9 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE:
 		flags = BLKDEV_ZERO_NOFALLBACK;
 		break;
+	case FALLOC_FL_WRITE_ZEROES:
+		flags = 0;
+		break;
 	default:
 		error = -EOPNOTSUPP;
 		goto fail;
-- 
2.46.1

[PATCH v2 9/9] ext4: add FALLOC_FL_WRITE_ZEROES support

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

Add support for FALLOC_FL_WRITE_ZEROES if the underlying device enable
the unmap write zeroes operation. This first allocates blocks as
unwritten, then issues a zero command outside of the running journal
handle, and finally converts them to a written state.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
---
 fs/ext4/extents.c           | 66 ++++++++++++++++++++++++++++++-------
 include/trace/events/ext4.h |  3 +-
 2 files changed, 57 insertions(+), 12 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index b543a46fc809..b43aa82c1b39 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4501,6 +4501,8 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
 	struct ext4_map_blocks map;
 	unsigned int credits;
 	loff_t epos, old_size = i_size_read(inode);
+	unsigned int blkbits = inode->i_blkbits;
+	bool alloc_zero = false;
 
 	BUG_ON(!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS));
 	map.m_lblk = offset;
@@ -4513,6 +4515,17 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
 	if (len <= EXT_UNWRITTEN_MAX_LEN)
 		flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
 
+	/*
+	 * Do the actual write zero during a running journal transaction
+	 * costs a lot. First allocate an unwritten extent and then
+	 * convert it to written after zeroing it out.
+	 */
+	if (flags & EXT4_GET_BLOCKS_ZERO) {
+		flags &= ~EXT4_GET_BLOCKS_ZERO;
+		flags |= EXT4_GET_BLOCKS_UNWRIT_EXT;
+		alloc_zero = true;
+	}
+
 	/*
 	 * credits to insert 1 extent into extent tree
 	 */
@@ -4549,9 +4562,7 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
 		 * allow a full retry cycle for any remaining allocations
 		 */
 		retries = 0;
-		map.m_lblk += ret;
-		map.m_len = len = len - ret;
-		epos = (loff_t)map.m_lblk << inode->i_blkbits;
+		epos = (loff_t)(map.m_lblk + ret) << blkbits;
 		inode_set_ctime_current(inode);
 		if (new_size) {
 			if (epos > new_size)
@@ -4571,6 +4582,21 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
 		ret2 = ret3 ? ret3 : ret2;
 		if (unlikely(ret2))
 			break;
+
+		if (alloc_zero &&
+		    (map.m_flags & (EXT4_MAP_MAPPED | EXT4_MAP_UNWRITTEN))) {
+			ret2 = ext4_issue_zeroout(inode, map.m_lblk, map.m_pblk,
+						  map.m_len);
+			if (likely(!ret2))
+				ret2 = ext4_convert_unwritten_extents(NULL,
+					inode, (loff_t)map.m_lblk << blkbits,
+					(loff_t)map.m_len << blkbits);
+			if (ret2)
+				break;
+		}
+
+		map.m_lblk += ret;
+		map.m_len = len = len - ret;
 	}
 	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
 		goto retry;
@@ -4636,7 +4662,11 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 	if (end_lblk > start_lblk) {
 		ext4_lblk_t zero_blks = end_lblk - start_lblk;
 
-		flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN | EXT4_EX_NOCACHE);
+		if (mode & FALLOC_FL_WRITE_ZEROES)
+			flags = EXT4_GET_BLOCKS_CREATE_ZERO | EXT4_EX_NOCACHE;
+		else
+			flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
+				  EXT4_EX_NOCACHE);
 		ret = ext4_alloc_file_blocks(file, start_lblk, zero_blks,
 					     new_size, flags);
 		if (ret)
@@ -4745,11 +4775,18 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	if (IS_ENCRYPTED(inode) &&
 	    (mode & (FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_INSERT_RANGE)))
 		return -EOPNOTSUPP;
+	/*
+	 * Don't allow writing zeroes if the underlying device does not
+	 * enable the unmap write zeroes operation.
+	 */
+	if ((mode & FALLOC_FL_WRITE_ZEROES) &&
+	    !bdev_write_zeroes_unmap_sectors(inode->i_sb->s_bdev))
+		return -EOPNOTSUPP;
 
 	/* Return error if mode is not supported */
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
-		     FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
-		     FALLOC_FL_INSERT_RANGE))
+		     FALLOC_FL_ZERO_RANGE | FALLOC_FL_COLLAPSE_RANGE |
+		     FALLOC_FL_INSERT_RANGE | FALLOC_FL_WRITE_ZEROES))
 		return -EOPNOTSUPP;
 
 	inode_lock(inode);
@@ -4780,16 +4817,23 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	if (ret)
 		goto out_invalidate_lock;
 
-	if (mode & FALLOC_FL_PUNCH_HOLE)
+	switch (mode & FALLOC_FL_MODE_MASK) {
+	case FALLOC_FL_PUNCH_HOLE:
 		ret = ext4_punch_hole(file, offset, len);
-	else if (mode & FALLOC_FL_COLLAPSE_RANGE)
+		break;
+	case FALLOC_FL_COLLAPSE_RANGE:
 		ret = ext4_collapse_range(file, offset, len);
-	else if (mode & FALLOC_FL_INSERT_RANGE)
+		break;
+	case FALLOC_FL_INSERT_RANGE:
 		ret = ext4_insert_range(file, offset, len);
-	else if (mode & FALLOC_FL_ZERO_RANGE)
+		break;
+	case FALLOC_FL_ZERO_RANGE:
+	case FALLOC_FL_WRITE_ZEROES:
 		ret = ext4_zero_range(file, offset, len, mode);
-	else
+		break;
+	default:
 		ret = -EOPNOTSUPP;
+	}
 
 out_invalidate_lock:
 	filemap_invalidate_unlock(mapping);
diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index 156908641e68..6f9cf2811733 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -92,7 +92,8 @@ TRACE_DEFINE_ENUM(ES_REFERENCED_B);
 	{ FALLOC_FL_KEEP_SIZE,		"KEEP_SIZE"},		\
 	{ FALLOC_FL_PUNCH_HOLE,		"PUNCH_HOLE"},		\
 	{ FALLOC_FL_COLLAPSE_RANGE,	"COLLAPSE_RANGE"},	\
-	{ FALLOC_FL_ZERO_RANGE,		"ZERO_RANGE"})
+	{ FALLOC_FL_ZERO_RANGE,		"ZERO_RANGE"},		\
+	{ FALLOC_FL_WRITE_ZEROES,	"WRITE_ZEROES"})
 
 TRACE_DEFINE_ENUM(EXT4_FC_REASON_XATTR);
 TRACE_DEFINE_ENUM(EXT4_FC_REASON_CROSS_RENAME);
-- 
2.46.1

Re: [PATCH v2 1/9] block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 2/9] nvme: set max_hw_wzeroes_unmap_sectors if device supports DEAC bit

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 3/9] nvmet: set WZDS and DRB if device enables unmap write zeroes operation

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 0/9] fallocate: introduce FALLOC_FL_WRITE_ZEROES flag

[Christian Brauner]

On Thu, 19 Jun 2025 19:17:57 +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
> 
> Changes since v1:
>  - Rebase codes on 6.16-rc2.
>  - Use max_{hw|user}_wzeroes_unmap_sectors queue limits instead of
>    BLK_FEAT_WRITE_ZEROES_UNMAP feature to represent the status of the
>    unmap write zeroes operation as Christoph and Darrick suggested. This
>    redoes the first 5 patches, so remove all the reviewed-by tags,
>    please review them again.
>  - Simplify the description of FALLOC_FL_WRITE_ZEROES in patch 06 as
>    Darrick suggested.
>  - Revise the check order of FALLOC_FL_WRITE_ZEROES in patch 08 as
>    Christoph suggested.
> Changes since RFC v4:
>  - Rebase codes on 6.16-rc1.
>  - Add a new queue_limit flag, and change the write_zeroes_unmap sysfs
>    interface to RW mode. User can disable the unmap write zeroes
>    operation by writing '0' to it when the operation is slow.
>  - Modify the documentation of write_zeroes_unmap sysfs interface as
>    Martin suggested.
>  - Remove the statx interface.
>  - Make the bdev and ext4 don't allow to submit FALLOC_FL_WRITE_ZEROES
>    if the block device does not enable the unmap write zeroes operation,
>    it should return -EOPNOTSUPP.
> Changes sicne RFC v3:
>  - Rebase codes on 6.15-rc2.
>  - Add a note in patch 1 to indicate that the unmap write zeros command
>    is not always guaranteed as Christoph suggested.
>  - Rename bdev_unmap_write_zeroes() helper and move it to patch 1 as
>    Christoph suggested.
>  - Introduce a new statx attribute flag STATX_ATTR_WRITE_ZEROES_UNMAP as
>    Christoph and Christian suggested.
>  - Exchange the order of the two patches that modified
>    blkdev_fallocate() as Christoph suggested.
> Changes since RFC v2:
>  - Rebase codes on next-20250314.
>  - Add support for nvme multipath.
>  - Add support for NVMeT with block device backing.
>  - Clear FALLOC_FL_WRITE_ZEROES if dm clear
>    limits->max_write_zeroes_sectors.
>  - Complement the counterpart userspace tools(util-linux and xfs_io)
>    and tests(blktests and xfstests), please see below for details.
> Changes since RFC v1:
>  - Switch to add a new write zeroes operation, FALLOC_FL_WRITE_ZEROES,
>    in fallocate, instead of just adding a supported flag to
>    FALLOC_FL_ZERO_RANGE.
>  - Introduce a new flag BLK_FEAT_WRITE_ZEROES_UNMAP to the block
>    device's queue limit features, and implement it on SCSI sd driver,
>    NVMe SSD driver and dm driver.
>  - Implement FALLOC_FL_WRITE_ZEROES on both the ext4 filesystem and
>    block device (bdev).
> 
> [...]

If needed, the branch can be declared stable and thus be used as base
for other work.

---

Applied to the vfs-6.17.fallocate branch of the vfs/vfs.git tree.
Patches in the vfs-6.17.fallocate branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.17.fallocate

[1/9] block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits
      https://git.kernel.org/vfs/vfs/c/2695a9b086fd
[2/9] nvme: set max_hw_wzeroes_unmap_sectors if device supports DEAC bit
      https://git.kernel.org/vfs/vfs/c/bf07c1180194
[3/9] nvmet: set WZDS and DRB if device enables unmap write zeroes operation
      https://git.kernel.org/vfs/vfs/c/a6c7ab5adcba
[4/9] scsi: sd: set max_hw_wzeroes_unmap_sectors if device supports SD_ZERO_*_UNMAP
      https://git.kernel.org/vfs/vfs/c/92372ed1cc88
[5/9] dm: clear unmap write zeroes limits when disabling write zeroes
      https://git.kernel.org/vfs/vfs/c/e383d550e716
[6/9] fs: introduce FALLOC_FL_WRITE_ZEROES to fallocate
      https://git.kernel.org/vfs/vfs/c/1ed1b5df86ec
[7/9] block: factor out common part in blkdev_fallocate()
      https://git.kernel.org/vfs/vfs/c/96433508c8c0
[8/9] block: add FALLOC_FL_WRITE_ZEROES support
      https://git.kernel.org/vfs/vfs/c/2b4e5f9b3eb9
[9/9] ext4: add FALLOC_FL_WRITE_ZEROES support
      https://git.kernel.org/vfs/vfs/c/51954e469396

Re: [PATCH v2 0/9] fallocate: introduce FALLOC_FL_WRITE_ZEROES flag

[Martin K. Petersen]

Zhang,

> This series implements the BLK_FEAT_WRITE_ZEROES_UNMAP feature and
> BLK_FLAG_WRITE_ZEROES_UNMAP_DISABLED flag for SCSI, NVMe and
> device-mapper drivers, and add the FALLOC_FL_WRITE_ZEROES and
> STATX_ATTR_WRITE_ZEROES_UNMAP support for ext4 and raw bdev devices.
> Any comments are welcome.

This looks OK to me.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen

Re: [PATCH v2 0/9] fallocate: introduce FALLOC_FL_WRITE_ZEROES flag

[Zhang Yi]

On 2025/6/23 23:08, Martin K. Petersen wrote:
> 
> Zhang,
> 
>> This series implements the BLK_FEAT_WRITE_ZEROES_UNMAP feature and
>> BLK_FLAG_WRITE_ZEROES_UNMAP_DISABLED flag for SCSI, NVMe and
>> device-mapper drivers, and add the FALLOC_FL_WRITE_ZEROES and
>> STATX_ATTR_WRITE_ZEROES_UNMAP support for ext4 and raw bdev devices.
>> Any comments are welcome.
> 
> This looks OK to me.
> 
> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
> 

Thank you, Martin and Christoph, for the patient review. I will update
my test patches next.

Best regards,
Yi.

Re: [PATCH v2 0/9] fallocate: introduce FALLOC_FL_WRITE_ZEROES flag

[Zhang Yi]

On 2025/6/23 18:46, Christian Brauner wrote:
> On Thu, 19 Jun 2025 19:17:57 +0800, Zhang Yi wrote:
>> From: Zhang Yi <yi.zhang@huawei.com>
>>
>> Changes since v1:
>>  - Rebase codes on 6.16-rc2.
>>  - Use max_{hw|user}_wzeroes_unmap_sectors queue limits instead of
>>    BLK_FEAT_WRITE_ZEROES_UNMAP feature to represent the status of the
>>    unmap write zeroes operation as Christoph and Darrick suggested. This
>>    redoes the first 5 patches, so remove all the reviewed-by tags,
>>    please review them again.
>>  - Simplify the description of FALLOC_FL_WRITE_ZEROES in patch 06 as
>>    Darrick suggested.
>>  - Revise the check order of FALLOC_FL_WRITE_ZEROES in patch 08 as
>>    Christoph suggested.
>> Changes since RFC v4:
>>  - Rebase codes on 6.16-rc1.
>>  - Add a new queue_limit flag, and change the write_zeroes_unmap sysfs
>>    interface to RW mode. User can disable the unmap write zeroes
>>    operation by writing '0' to it when the operation is slow.
>>  - Modify the documentation of write_zeroes_unmap sysfs interface as
>>    Martin suggested.
>>  - Remove the statx interface.
>>  - Make the bdev and ext4 don't allow to submit FALLOC_FL_WRITE_ZEROES
>>    if the block device does not enable the unmap write zeroes operation,
>>    it should return -EOPNOTSUPP.
>> Changes sicne RFC v3:
>>  - Rebase codes on 6.15-rc2.
>>  - Add a note in patch 1 to indicate that the unmap write zeros command
>>    is not always guaranteed as Christoph suggested.
>>  - Rename bdev_unmap_write_zeroes() helper and move it to patch 1 as
>>    Christoph suggested.
>>  - Introduce a new statx attribute flag STATX_ATTR_WRITE_ZEROES_UNMAP as
>>    Christoph and Christian suggested.
>>  - Exchange the order of the two patches that modified
>>    blkdev_fallocate() as Christoph suggested.
>> Changes since RFC v2:
>>  - Rebase codes on next-20250314.
>>  - Add support for nvme multipath.
>>  - Add support for NVMeT with block device backing.
>>  - Clear FALLOC_FL_WRITE_ZEROES if dm clear
>>    limits->max_write_zeroes_sectors.
>>  - Complement the counterpart userspace tools(util-linux and xfs_io)
>>    and tests(blktests and xfstests), please see below for details.
>> Changes since RFC v1:
>>  - Switch to add a new write zeroes operation, FALLOC_FL_WRITE_ZEROES,
>>    in fallocate, instead of just adding a supported flag to
>>    FALLOC_FL_ZERO_RANGE.
>>  - Introduce a new flag BLK_FEAT_WRITE_ZEROES_UNMAP to the block
>>    device's queue limit features, and implement it on SCSI sd driver,
>>    NVMe SSD driver and dm driver.
>>  - Implement FALLOC_FL_WRITE_ZEROES on both the ext4 filesystem and
>>    block device (bdev).
>>
>> [...]
> 
> If needed, the branch can be declared stable and thus be used as base
> for other work.
> 
> ---
> 
> Applied to the vfs-6.17.fallocate branch of the vfs/vfs.git tree.
> Patches in the vfs-6.17.fallocate branch should appear in linux-next soon.
> 
> Please report any outstanding bugs that were missed during review in a
> new review to the original patch series allowing us to drop it.
> 
> It's encouraged to provide Acked-bys and Reviewed-bys even though the
> patch has now been applied. If possible patch trailers will be updated.
> 
> Note that commit hashes shown below are subject to change due to rebase,
> trailer updates or similar. If in doubt, please check the listed branch.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> branch: vfs-6.17.fallocate

Hi Christian,

I noticed that this patch series doesn't appear to be merged into this
branch. Just wondering if it might have been missed?

Best regards,
Yi.

> 
> [1/9] block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits
>       https://git.kernel.org/vfs/vfs/c/2695a9b086fd
> [2/9] nvme: set max_hw_wzeroes_unmap_sectors if device supports DEAC bit
>       https://git.kernel.org/vfs/vfs/c/bf07c1180194
> [3/9] nvmet: set WZDS and DRB if device enables unmap write zeroes operation
>       https://git.kernel.org/vfs/vfs/c/a6c7ab5adcba
> [4/9] scsi: sd: set max_hw_wzeroes_unmap_sectors if device supports SD_ZERO_*_UNMAP
>       https://git.kernel.org/vfs/vfs/c/92372ed1cc88
> [5/9] dm: clear unmap write zeroes limits when disabling write zeroes
>       https://git.kernel.org/vfs/vfs/c/e383d550e716
> [6/9] fs: introduce FALLOC_FL_WRITE_ZEROES to fallocate
>       https://git.kernel.org/vfs/vfs/c/1ed1b5df86ec
> [7/9] block: factor out common part in blkdev_fallocate()
>       https://git.kernel.org/vfs/vfs/c/96433508c8c0
> [8/9] block: add FALLOC_FL_WRITE_ZEROES support
>       https://git.kernel.org/vfs/vfs/c/2b4e5f9b3eb9
> [9/9] ext4: add FALLOC_FL_WRITE_ZEROES support
>       https://git.kernel.org/vfs/vfs/c/51954e469396

Re: [PATCH v2 0/9] fallocate: introduce FALLOC_FL_WRITE_ZEROES flag

[Christian Brauner]

On Thu, Jul 03, 2025 at 11:35:41AM +0800, Zhang Yi wrote:
> On 2025/6/23 18:46, Christian Brauner wrote:
> > On Thu, 19 Jun 2025 19:17:57 +0800, Zhang Yi wrote:
> >> From: Zhang Yi <yi.zhang@huawei.com>
> >>
> >> Changes since v1:
> >>  - Rebase codes on 6.16-rc2.
> >>  - Use max_{hw|user}_wzeroes_unmap_sectors queue limits instead of
> >>    BLK_FEAT_WRITE_ZEROES_UNMAP feature to represent the status of the
> >>    unmap write zeroes operation as Christoph and Darrick suggested. This
> >>    redoes the first 5 patches, so remove all the reviewed-by tags,
> >>    please review them again.
> >>  - Simplify the description of FALLOC_FL_WRITE_ZEROES in patch 06 as
> >>    Darrick suggested.
> >>  - Revise the check order of FALLOC_FL_WRITE_ZEROES in patch 08 as
> >>    Christoph suggested.
> >> Changes since RFC v4:
> >>  - Rebase codes on 6.16-rc1.
> >>  - Add a new queue_limit flag, and change the write_zeroes_unmap sysfs
> >>    interface to RW mode. User can disable the unmap write zeroes
> >>    operation by writing '0' to it when the operation is slow.
> >>  - Modify the documentation of write_zeroes_unmap sysfs interface as
> >>    Martin suggested.
> >>  - Remove the statx interface.
> >>  - Make the bdev and ext4 don't allow to submit FALLOC_FL_WRITE_ZEROES
> >>    if the block device does not enable the unmap write zeroes operation,
> >>    it should return -EOPNOTSUPP.
> >> Changes sicne RFC v3:
> >>  - Rebase codes on 6.15-rc2.
> >>  - Add a note in patch 1 to indicate that the unmap write zeros command
> >>    is not always guaranteed as Christoph suggested.
> >>  - Rename bdev_unmap_write_zeroes() helper and move it to patch 1 as
> >>    Christoph suggested.
> >>  - Introduce a new statx attribute flag STATX_ATTR_WRITE_ZEROES_UNMAP as
> >>    Christoph and Christian suggested.
> >>  - Exchange the order of the two patches that modified
> >>    blkdev_fallocate() as Christoph suggested.
> >> Changes since RFC v2:
> >>  - Rebase codes on next-20250314.
> >>  - Add support for nvme multipath.
> >>  - Add support for NVMeT with block device backing.
> >>  - Clear FALLOC_FL_WRITE_ZEROES if dm clear
> >>    limits->max_write_zeroes_sectors.
> >>  - Complement the counterpart userspace tools(util-linux and xfs_io)
> >>    and tests(blktests and xfstests), please see below for details.
> >> Changes since RFC v1:
> >>  - Switch to add a new write zeroes operation, FALLOC_FL_WRITE_ZEROES,
> >>    in fallocate, instead of just adding a supported flag to
> >>    FALLOC_FL_ZERO_RANGE.
> >>  - Introduce a new flag BLK_FEAT_WRITE_ZEROES_UNMAP to the block
> >>    device's queue limit features, and implement it on SCSI sd driver,
> >>    NVMe SSD driver and dm driver.
> >>  - Implement FALLOC_FL_WRITE_ZEROES on both the ext4 filesystem and
> >>    block device (bdev).
> >>
> >> [...]
> > 
> > If needed, the branch can be declared stable and thus be used as base
> > for other work.
> > 
> > ---
> > 
> > Applied to the vfs-6.17.fallocate branch of the vfs/vfs.git tree.
> > Patches in the vfs-6.17.fallocate branch should appear in linux-next soon.
> > 
> > Please report any outstanding bugs that were missed during review in a
> > new review to the original patch series allowing us to drop it.
> > 
> > It's encouraged to provide Acked-bys and Reviewed-bys even though the
> > patch has now been applied. If possible patch trailers will be updated.
> > 
> > Note that commit hashes shown below are subject to change due to rebase,
> > trailer updates or similar. If in doubt, please check the listed branch.
> > 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> > branch: vfs-6.17.fallocate
> 
> Hi Christian,
> 
> I noticed that this patch series doesn't appear to be merged into this
> branch. Just wondering if it might have been missed?

Dammit, my script missed to push the branch. Fixed now. Thanks for
checking!

Re: [PATCH v2 1/9] block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits

[John Garry]

On 19/06/2025 12:17, Zhang Yi wrote:
>   }
> @@ -333,6 +335,12 @@ int blk_validate_limits(struct queue_limits *lim)
>   	if (!lim->max_segments)
>   		lim->max_segments = BLK_MAX_SEGMENTS;
>   
> +	if (lim->max_hw_wzeroes_unmap_sectors &&
> +	    lim->max_hw_wzeroes_unmap_sectors != lim->max_write_zeroes_sectors)
> +		return -EINVAL;

JFYI, I noticed that I am failing this check in raid0_set_limits() -> 
queue_limits_set() -> queue_limits_commit_update() -> 
blk_validate_limits() for v6.17-rc2

The raid0 array consists of NVMe partitions. Here 
lim->max_hw_wzeroes_unmap_sectors = 4096 and 
lim->max_write_zeroes_sectors = 0 values for the failure, above.

john@raspberrypi:~ $ cat /sys/block/nvme0n1/queue/write_zeroes_max_bytes
2097152
john@raspberrypi:~ $ cat 
/sys/block/nvme0n1/queue/write_zeroes_unmap_max_bytes
2097152
john@raspberrypi:~ $ cat
/sys/block/nvme0n1/queue/write_zeroes_unmap_max_hw_bytes
2097152
john@raspberrypi:~ $



> +	lim->max_wzeroes_unmap_sectors = min(lim->max_hw_wzeroes_unmap_sectors,
> +			lim->max_user_wzeroes_unmap_sectors);
> +
>   	lim->max_discard_sectors =
>   		min(lim->max_hw_discard_sectors, lim->max_user_discard_sectors);
>   
> @@ -418,10 +426,11 @@ int blk_set_default_limits(struct queue_limits *lim)

Re: [PATCH v2 1/9] block: introduce max_{hw|user}_wzeroes_unmap_sectors to queue limits

[Zhang Yi]

On 8/21/2025 8:55 PM, John Garry wrote:
> On 19/06/2025 12:17, Zhang Yi wrote:
>>   }
>> @@ -333,6 +335,12 @@ int blk_validate_limits(struct queue_limits *lim)
>>       if (!lim->max_segments)
>>           lim->max_segments = BLK_MAX_SEGMENTS;
>>   +    if (lim->max_hw_wzeroes_unmap_sectors &&
>> +        lim->max_hw_wzeroes_unmap_sectors != lim->max_write_zeroes_sectors)
>> +        return -EINVAL;
> 
> JFYI, I noticed that I am failing this check in raid0_set_limits() -> queue_limits_set() -> queue_limits_commit_update() -> blk_validate_limits() for v6.17-rc2
> 
> The raid0 array consists of NVMe partitions. Here lim->max_hw_wzeroes_unmap_sectors = 4096 and lim->max_write_zeroes_sectors = 0 values for the failure, above.
> 
> john@raspberrypi:~ $ cat /sys/block/nvme0n1/queue/write_zeroes_max_bytes
> 2097152
> john@raspberrypi:~ $ cat /sys/block/nvme0n1/queue/write_zeroes_unmap_max_bytes
> 2097152
> john@raspberrypi:~ $ cat
> /sys/block/nvme0n1/queue/write_zeroes_unmap_max_hw_bytes
> 2097152
> john@raspberrypi:~ $
> 
> 

Thank you for checking on this!

The problem is that raid0_set_limits() only sets max_write_zeroes_sectors
without synchronously setting max_hw_wzeroes_unmap_sectors. It appears
that all stacked drivers that call blk_set_stacking_limits() to
initialize stacked limits but independently adjust
max_write_zeroes_sectors are problematic, including all md drivers and
drbd. These drivers need to update max_hw_wzeroes_unmap_sectors as well, I
will send out a fix soon.

Thanks,
Yi.

> 
>> +    lim->max_wzeroes_unmap_sectors = min(lim->max_hw_wzeroes_unmap_sectors,
>> +            lim->max_user_wzeroes_unmap_sectors);
>> +
>>       lim->max_discard_sectors =
>>           min(lim->max_hw_discard_sectors, lim->max_user_discard_sectors);
>>   @@ -418,10 +426,11 @@ int blk_set_default_limits(struct queue_limits *lim)